1. Field of the Invention
The present invention relates generally to optical imaging systems and more particularly to an optical imaging system for forming an image of an object plane within a sample medium.
2. Description of the Prior Art
Generally, optical imaging systems form an image of the surface of an object. There is, however, an increasing need, especially within the medical arts, for optical systems that form high-quality images of a selected object plane within a sample medium. Generally, the sample medium is a human organ, such as, for example, the human eye. In the human eye the object plane may be selected to lie in the cornea or along the retina. High-quality images of the retina are vital to diagnosing a large variety of medical conditions.
The process of forming an optical image of an object plane includes the steps of illuminating the object plane, collecting the reflected light emanating from the object plane, and focusing the collected light on an image plane. Typically, these optical systems include lenses and mirrors to accomplish the various functions of illuminating, collecting, and focusing.
Forming a high-quality image of an object plane within a sample medium requires special techniques to overcome the deterioration of the image due to scattering of the illuminating light from the region of the sample medium external to the object plane. This scattered light is collected and focused along with light emanating from the object plane and thus obfuscates the image formed of the object plane.
Existing systems for imaging an object plane within a sample medium generally include an illuminating slit, for illuminating a region of the object plane, a viewing slit, for viewing the illuminated region of the object plane, and optics configured so that the region of the sample medium external to the object plane is not viewable through the viewing slit. Accordingly, most of the light scattered by the external sample medium will not pass through the viewing slit. Only the light passing through the viewing slit is focused on the image plane, thus, the obfuscation of the image of the object plane by this scattered light is substantially obviated.
The above-described systems only provide an image of a narrow, slit-shaped region of the object plane at a given time. To view a significant region of the object plane the slit is scanned across the object plane. Two examples of the above-described system are disclosed in U.S. Pat. Nos. 3,547,512 and 4,170,398 issued to Baer and Koester, respectively. In Baer, the illuminating slit and viewing slit are formed in planar diaphragms disposed substantially at right angles to each other. The scanning of the slits is accomplished by oscillating the diaphragms about an axis. In Koester, the illuminating and viewing slits are formed in planar diaphragms disposed substantially parallel to each other. In Koester the scanning of the slit is accomplished by a system utilizing a rotating mirror.
In U.S. Pat. No. 4,135,791 issued to Govignon, an optical fiber arrangement is utilized to scan an illumination beam along the retina and the illumination beam is synchronously viewed through a slit in a rotating diaphragm.
The above-described systems provide a high-quality image of an object plane in a sample medium such as, for example, the retina of the human eye. However, these devices do not provide for selectable alternate functions such as illuminating and viewing through colored filters to perform chemical analysis, non-coincident illumination and viewing, and stereo image formation. These functions are vitally important in many applications. Additionally, functions such as flare control, auto-focusing, and eye position error indication are highly desirable.